Mast cells can be stimulated to secrete histamine by a variety of non-immunological agents. These secretagogues are believed to act independently of the IgE molecule and differ in this and several other significant ways from immunologic agents such as antigen or anti-IgE serum. Evidence accumulated over the past few years convincingly suggests an active role for several of these non-immunologic agents in the physiological regulation of mast cell function and raises the distinct possibility of new, as yet unknown, roles for the mast cell. The mechanisms by which these non-immunologic secretagogues activate and control mast cell secretion are only partially understood. It is the objective of this research proposal to study these mechanisms. For this, the characteristics of the Ca-entry mechanism activated by stimulation with non-immunologic secretagogues will be determined using the process of inactivation (i.e., the decay in Ca permeability). Initial experiments will characterize Ca movements in the absence of secretion using 45Ca efflux from cells loaded with 45Ca by stimulation. The specificity of the inactivation process, the effect of membrane potential, the cellular changes that may precede and/or accompany inactivation, recovery from inactivation, and whether non-immunologic and innumologic secretagogues activate a common Ca-"channel" mechanism will be determined. Secondly, the binding characteristics for non-immunologic secretagogues, the possibility of a common binding site, and whether "down regulation" of binding occurs during the inactivation process will be determined. Thirdly, the characteristics of the non-immunologic peptide secretagogues, neurotensin, bradykinin, and substance P. will be directly determined and compared to the more fully studied, synthetic secretagogue, compound 48/80. Fourth, non-immunologic agents are believed to act independently of the IgE molecule. This conjecture will be directly tested. Finally, the characteristics of the cellular Ca pool that is accessible to chelation and whether cellular Ca is released from a membrane fraction will be determined.